Helium charged refrigerator

ABSTRACT

A helium charged refrigerator is capable of cooling a refrigerator box to a temperature of 6° C. (43° F.) and the freezer compartment to a temperature of −9° C. (15° F.) when the ambient is at a temperature of 43° C. (110° F.). The total cubic area cooled is greater than or equal to six cubic feet. The unit includes a condenser, an evaporator, a liquid ammonia tube, and a gas heat exchanger. The liquid ammonia tube includes two vertical sections. The second section is downstream of the first and is noncontiguous with the heat exchanger so that no heat is exchanged between flowable fluids flowing in the second vertical section and in the heat exchanger. The heat exchanger includes modifications to its inner and outer tubes to produce an increase in surface area of the corresponding surface.

REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/450,237, filed Mar. 8, 2011, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to gas absorption refrigeration coolingsystems and specifically to a helium gas charged refrigerator for arecreational vehicle (RV).

2. Description of the Prior Art

The cooling cycle of the typical diffusion-absorption refrigerationsystem starts with liquefied ammonia entering an evaporator at roomtemperature. The ammonia is mixed in the evaporator with hydrogen. Thepartial pressure of the hydrogen is used to regulate the total pressure,which in turn regulates the vapor pressure and thus the boiling point ofthe ammonia. The ammonia boils in the evaporator, providing the coolingrequired. The fluids are endlessly recirculated by gravity.

Hydrogen is assumed to be the optimum diffusion gas used indiffusion-absorption cooling systems because it is the lightest elementof the periodic table. It has an atomic weight of one, and its molecularweight is about the same. Hydrogen has always been the preferreddiffusion agent because its partial pressure, which regulates theoverall pressure of the closed system, is small and easily calculable.Hydrogen is predictable as the element moves between phase changes andsolution in the system as well.

Helium, on the other hand, has an atomic weight of two and is consideredineffective as a diffusion gas for such cooling systems. The moreweighty helium has a different partial pressure and requires a higherboiling temperature for the ammonia in a helium charged system.Refrigerators that operate outdoors at higher ambient temperatures havedifficulty reaching desirable cooling temperatures. Normal-sizeddiffusion-absorption type refrigerators where the total area chilled isabout eight cubic feet, for example, cannot use helium and meetapplicable ANSI standards.

Hydrogen, however, is volatile and extremely dangerous. Fire andexplosion have produced a need for an alternative diffusion or charginggas. Prior refrigerators that use helium as a charging gas, e.g., hotelmini bar refrigerators, are for low ambient temperatures (i.e., 32° C.(90° F.) or lower). Such applications have a nominal ambient temperaturerating of 25° C. (77° F.). The ANSI standard applicable to RV gasabsorption refrigeration cooling systems, however, requires thefollowing specifications at an ambient temperature of 43° C. (110° F.):(i) the refrigerator compartment cooled to a temperature of at least 6°C. (43° F.) and (ii) the freezer compartment cooled to a temperature ofat least −9° C. (15° F.).

The invention has overcome the perceived barriers to using helium as adiffusion gas for normal-sized refrigerators and results in arefrigerator that meets the applicable ANSI standards—that is, theinventive helium charged system provides desirable freezer/refrigerationtemperatures for larger refrigerators operative where the ambient is nottemperature controlled.

SUMMARY OF THE INVENTION

The disadvantages heretofore associated with the prior art are overcomeby the inventive RV refrigeration cooling system using helium as thecharging gas. The novel system is for a refrigerator of the type thatrelies upon gravity to move fluid through a closed fluid system for heatexchange between an ammonia solution and a diffusion or charging gas.Such a refrigerator has a freezer evaporator, including a freezer box, acabinet evaporator, including a refrigerator box, an absorber vesseldownstream of the freezer and cabinet evaporators, and a liquid heatexchanger downstream of the absorber vessel.

The new refrigerator includes a diffusion-absorption refrigerationassembly that uses helium as a diffusion gas. The refrigeration assemblyincludes a condenser, an evaporator, a liquid ammonia tube, and a gasheat exchanger.

In one aspect of the invention, the liquid ammonia tube may include afirst vertical section with an inlet and a second vertical sectiondownstream of the first. The refrigerator may include a freezer boxdefining a first cubic area and a refrigerator box defining a secondcubic area.

In another aspect, the sum of the first and second cubic areas may beequal to or greater than six cubic feet such that the assembly iscapable of cooling the refrigerator box to a temperature of 6° C. (43°F.) and the freezer compartment to a temperature of −9° C. (15° F.) whenthe ambient is at a temperature of 43° C. (110° F.).

In yet another aspect, the heat exchanger includes inner and outertubes, said inner tube having an outer surface, and said outer tubehaving an inner surface, said outer and inner surfaces each being shapedto produce an increase in surface area of the corresponding surface.

One object of the invention is to provide a novel refrigerator having adiffusion-absorption refrigeration assembly that uses helium as adiffusion gas instead of hydrogen and thus is safe if the system isruptured and gas escapes. It has heretofore not been possible for ahelium charged refrigerator to cool eight (8) cubic feet, that is, thesize of the refrigerator box to a temperature of 6° C. (43° F.) and thesize of the freezer compartment to a temperature of −9° C. (15° F.) whenthe ambient is at a temperature of 43° C. (110° F.). In other words, thenew refrigerator meets ANSI standards for cooling larger refrigeratorswhere the ambient is not temperature controlled. Related objects andadvantages of the invention will be apparent from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of the invention, both as to its structure and operation,may be obtained by a review of the accompanying drawings, in which:

FIG. 1 is an isometric view of a refrigerator of the invention showingthe freezer box and the refrigerator box;

FIG. 2 is a diagrammatic illustration of a typical prior art absorptionsystem;

FIG. 3 is a diagrammatic drawing of the diffusion-absorptionrefrigeration assembly of the invention;

FIG. 4 is a partial cutaway isometric view of an embodiment of the heatexchanger of the invention;

FIG. 4A is an enlarged view of the outer surface of the inner tube ofthe heat exchanger of the invention; and

FIG. 4B is an enlarged view of the inner surface of the outer tube ofthe heat exchanger of the invention.

DETAILED DESCRIPTION OF INVENTION

The invention is a refrigerator 10 having a diffusion-absorptionrefrigeration assembly 20 that uses helium as a diffusion gas instead ofhydrogen. As shown in FIG. 3, the refrigeration assembly includes acondenser 22, an evaporator (freezer 24, cabinet 26), a liquid ammoniatube 25, and a gas heat exchanger 27. The liquid ammonia tube has afirst vertical section 30 with an inlet 31, a second vertical section 32downstream of the first, and an intermediate section 34 downstream ofthe second vertical section.

The second vertical section 32 does not touch the heat exchanger 27. Noheat is exchanged between flowable fluids flowing in the second verticalsection and in the heat exchanger as a result. Additionally, theintermediate section 34 is contiguous with the heat exchanger 27 so thatheat is exchanged between flowable fluids flowing in the intermediatesection and in the heat exchanger.

Referring to FIG. 1, the refrigerator 10 has a freezer box 12 defining afirst cubic area and a refrigerator box 14 defining a second cubic area.In one embodiment, the sum of the first and second cubic areas is equalto about six (6) cubic feet. In a more preferred embodiment the sum ofthe first and second cubic areas is equal to about eight (8) cubic feet.

With reference to FIG. 2, the function of a typical absorption systemwill now be described. The rich solution leaves the absorber vessel 210and passes through the liquid heat exchanger 212 to the bottom of thepump tube 214. The heat source (gas or electric) 216 causes thetemperature of the solution to rise. This temperature increase causesammonia and some water vapor to be driven out of the solution, formingvapor bubbles which push columns of liquid up the pump tube. The liquidfalls downward through the rectifier 218 where the temperature isincreased causing additional ammonia vapor to be released. The remainingliquid is now a weak ammonia solution and flows through the externalshell of the liquid heat exchanger 212 where it transfers its residualheat to the rich solution and enters the top of the absorber coil 220 ata reduced temperature.

The ammonia/water vapor passes through the water separator 222 whosereduced temperature causes any water vapor to liquefy and join the weaksolution in the boiler 224. The ammonia vapor enters the condenser 226where it condenses to hot liquid ammonia. The liquid ammonia enters thetubular coil of the freezer and cabinet evaporators 228, 230 and wetsthe internal surface of the tubes.

As the weak gas passes over the wetted surface of the evaporator tubing,the liquid ammonia evaporates into the hydrogen, creating an initialrefrigeration temperature of about −20° F. The weight of the hydrogenand ammonia mixture is heavier than that of weak gas. Consequently, itfalls through the gas heat exchanger into the top of the absorber vessel210. From this point it enters the bottom of the absorber coil.

As this mixture travels up through the absorber it contacts the weaksolution entering the top of the absorber from the boiler. As the weaksolution drops through the absorber it absorbs the ammonia from theammonia/hydrogen mixture. The relatively pure hydrogen passes throughthe hydrogen circuit to the evaporator and now the rich solution fallsto the bottom on the absorber vessel where the cycle starts again.

Referring to FIG. 3, the rich ammonia water solution leaves the absorbervessel 40 and passes through the liquid heat exchanger to the bottom ofthe pump tube. The heat source (gas or electric) 44 causes thetemperature of the solution to rise. This temperature increase causesammonia and some water vapor to be driven out of the solution, formingvapor bubbles, which push columns of liquid up the pump tube. The liquidfalls downward through the rectifier 46 where the temperature isincreased causing additional ammonia vapor to be released. The remainingliquid is now a weak ammonia solution and flows through the externalshell of the liquid heat exchanger 42 where it transfers its residualheat to the rich solution and enters the top of the absorber coil at areduced temperature.

The ammonia/water vapor passes through the water separator 48 whosereduced temperature causes a water vapor to liquefy and join the weaksolution in the boiler 50. The ammonia vapor enters the condenser 22where it condenses to hot liquid ammonia. The liquid ammonia enters thetubular coil of the freezer and cabinet evaporators 24, 26 and wets theinternal surface of the tubes. Referring to FIGS. 4, 4A and 4B, theincreased tube volume of Applicant's device accommodates the increasedweight of the helium over hydrogen. Smaller heat exchange tubes suitablefor hydrogen provide restriction for the larger helium molecules.

Additionally, a second heat exchanger 60 is between the freezer and thecabinet evaporators 24, 26. In one embodiment, the new heat exchangeconduit section 60 includes a first tube 61 having an outer surface 62and a second tube 63 having an inner surface 64. The new heat exchangeconduit section 60 is connected “stream wise” into the overallabsorption system. The first tube 61 has an outer diameter smaller thanthe inner diameter of the second tube 63 so that the first tube can bepositioned inside the second to define a space that has a crosssectional area and a length. Applicant's have discovered that to meetthe ANSI RV refrigeration standards (i.e., the refrigerator compartmentcooled to at least 6° C. (43° F.) and the freezer compartment cooled toat least −9° C. (15° F.) when the ambient is at 43° C. (110° F.)), theinner diameters of the tubes have to be substantially modified if heliumis used as the diffusion gas.

In one embodiment, therefore, the cross sectional area between the innersurface of the outer tube and the outer surface of the inner tube isabout 200 square millimeters. In another embodiment, the outer diameterof the inner tube is increased, thus reducing the cross-sectional areabetween the inner and outer tubes by twenty percent (20%). In a morepreferred embodiment, the outer diameter of the inner tube 61 is betweenabout 14 and 16 millimeters and the outer diameter of the outer tube 63is between about 25 and 27 millimeters; however, other combinations ofinner and outer tube diameters may be derived that would serve tocompensate for the larger helium molecules. Thus, the evaporator tubesof the new system are specially sized in proportion to the other tubesso that the larger gaseous helium molecules are effective in replacinghydrogen as the diffusion gas.

The assembly 20, is thus capable of cooling the refrigerator box 14 to atemperature of 6° C. (43° F.) and the freezer box 12 to a temperature of−9° C. (15° F.) when the ambient is at a temperature of 43° C. (110°F.). The assembly meets applicable ANSI standards.

The outer and inner surfaces 62, 64 are preferably shaped, respectively,in a manner to increase their area. The example shown in FIGS. 4A and 4Bmay be construed as a serrated shape. Those skilled in the art willappreciate that any one of a number of shapes may be formed in thesurfaces to increase their surface area. Fins may be another example ofa shape contemplated.

The shaped outer surface of the tubes increase the surface area exposed,as shown in FIGS. 4A-4B. As the weak gas passes over the wetted surfaceof the evaporator tubing, the liquid ammonia evaporates into the helium.As the ammonia continues to evaporate into the helium, the partialpressure of ammonia continues to rise slowly. As the ammonia pressurerises, the evaporation temperature also rises.

The new heat exchanger conduit section 60 of the new system between therefrigerator and freezer compartments pre-cools the liquid ammoniabefore it enters the freezer's evaporators section. This prevents hotliquid ammonia from injecting heat into the coldest portion of theevaporator and helps lower the temperature in the evaporator, whichimproves the overall cooling performance.

As the ammonia continues to evaporate into the helium, the partialpressure of ammonia continues to rise slowly. As the ammonia pressurerises the evaporation temperature also rises. This increase in ammoniapartial pressure raises the evaporation temperature steadily downthrough the evaporator. The weight of the helium and ammonia mixture isheavier than that of a weak gas. Hence, it falls through the gas heatexchanger into the top of the absorber vessel. From this point it entersthe bottom of the absorber coil.

As this mixture travels up through the absorber it contacts the weaksolution entering the top of the absorber from the boiler. As the weaksolution drops through the absorber, it absorbs the ammonia from theammonia/helium mixture. The relatively pure helium passes through thehelium circuit to the evaporator and now the rich solution falls to thebottom of the absorber vessel where the cycle starts again.

A significant advantage of the new helium charged cooling system in RVrefrigeration applications is the increased safety of the refrigerator10. A hydrogen charged gas absorption system may create a serious fireor explosion if the closed fluid system is compromised.

For the purposes of promoting an understanding of the principles of theinvention, specific embodiments have been described. It shouldnevertheless be understood that the description is intended to beillustrative and not restrictive in character, and that no limitation ofthe scope of the invention is intended. Any alterations and furthermodifications in the described components, elements, processes, ordevices, and any further applications of the principles of the inventionas described herein, are contemplated as would normally occur to oneskilled in the art to which the invention relates.

1. A refrigerator having a diffusion-absorption refrigeration assembly that uses helium as a diffusion gas, the refrigeration assembly comprising, a condenser, an evaporator, a liquid ammonia tube, and a gas heat exchanger, wherein the liquid ammonia tube comprising a first vertical section with an inlet, and a second vertical section downstream of the first.
 2. A refrigerator according to claim 1, wherein the second vertical section of the liquid ammonia tube being noncontiguous with said heat exchanger, wherein no heat is exchanged between flowable fluids flowing in said second vertical section and in said heat exchanger.
 3. A refrigerator according to claim 1, wherein said liquid ammonia tube further comprising an intermediate section downstream of the second vertical section, said intermediate section being contiguous with said heat exchanger, wherein heat is exchanged between flowable fluids flowing in said intermediate section and in said heat exchanger.
 4. A refrigerator according to claim 3, wherein said liquid ammonia tube further comprising a freezer section upstream of the intermediate section, said freezer section being contiguous with said heat exchanger, wherein heat is exchanged between flowable fluids flowing in said freezer section and in said heat exchanger.
 5. A refrigerator according to claim 4, wherein the second vertical section of the liquid ammonia tube being noncontiguous with said heat exchanger, wherein no heat is exchanged between flowable fluids flowing in said second vertical section and in said heat exchanger.
 6. A refrigerator having a diffusion-absorption refrigeration assembly that uses helium as a diffusion gas, the refrigeration assembly comprising, a condenser, an evaporator, a liquid ammonia tube, and a gas heat exchanger, wherein the liquid ammonia tube comprising a first vertical section with an inlet, and a second vertical section downstream of the first, said refrigerator having a freezer box defining a first cubic area, and a refrigerator box defining a second cubic area, the sum of said first and second cubic areas being equal to or greater than six cubic feet, wherein said assembly being capable of cooling the refrigerator box to a temperature of 6° C. (43° F.) and the freezer compartment to a temperature of −9° C. (15° F.) when the ambient is at a temperature of 43° C. (110° F.).
 7. A refrigerator according to claim 6, wherein the heat exchanger includes inner and outer tubes, said inner tube having an outer surface, and said outer tube having an inner surface, said outer and inner surfaces each being shaped to produce an increase in surface area of the corresponding surface.
 8. A refrigerator having a diffusion-absorption refrigeration assembly that uses helium as a diffusion gas, the refrigeration assembly comprising, a condenser, an evaporator, a liquid ammonia tube, a gas heat exchanger, wherein the liquid ammonia tube comprising a first vertical section with an inlet, and a second vertical section downstream of the first, said refrigerator having a freezer box defining a first cubic area, and a refrigerator box defining a second cubic area, the sum of said first and second cubic areas being equal to or greater than six cubic feet, wherein said assembly being capable of cooling the refrigerator box to a temperature of 6° C. (43° F.) and the freezer compartment to a temperature of −9° C. (15° F.) when the ambient is at a temperature of 43° C. (110° F.), wherein the second vertical section of the liquid ammonia tube being noncontiguous with said heat exchanger, wherein no heat is exchanged between flowable fluids flowing in said second vertical section and in said heat exchanger.
 9. A refrigerator according to claim 8, wherein the heat exchanger includes inner and outer tubes, said inner tube having an outer surface, and said outer tube having an inner surface, said outer and inner surfaces each having serrations to produce an increase in surface area of the corresponding surface.
 10. A refrigerator according to claim 9, wherein said liquid ammonia tube further comprising an intermediate section downstream of the second vertical section, said intermediate section being contiguous with said heat exchanger, wherein heat is exchanged between flowable fluids flowing in said intermediate section and in said heat exchanger.
 11. A refrigerator according to claim 10, wherein the second vertical section of the liquid ammonia tube being noncontiguous with said heat exchanger, wherein no heat is exchanged between flowable fluids flowing in said second vertical section and in said heat exchanger.
 12. A refrigerator having a diffusion-absorption refrigeration assembly that uses helium as a diffusion gas, the refrigeration assembly comprising, a condenser, an evaporator, a liquid ammonia tube, and a gas heat exchanger, wherein the gas heat exchanger comprising an inner tube having and outer diameter of between about 14 and about 16 millimeters and an outer tube having an outer diameter of between about 25 and 27 millimeters, said refrigerator having a freezer box defining a first cubic area, and a refrigerator box defining a second cubic area, the sum of said first and second cubic areas being equal to or greater than six cubic feet, wherein said assembly being capable of cooling the refrigerator box to a temperature of 6° C. (43° F.) and the freezer compartment to a temperature of −9° C. (15° F.) when the ambient is at a temperature of 43° C. (110° F.).
 13. A refrigerator according to claim 12, wherein the liquid ammonia tube comprising a first vertical section with an inlet, and a second vertical section downstream of the first, wherein the second vertical section being noncontiguous with said heat exchanger, wherein no heat is exchanged between flowable fluids flowing in said second vertical section and in said heat exchanger.
 14. A refrigerator according to claim 13, wherein said liquid ammonia tube further comprising an intermediate section downstream of the second vertical section, said intermediate section being contiguous with said heat exchanger, wherein heat is exchanged between flowable fluids flowing in said intermediate section and in said heat exchanger.
 15. A refrigerator according to claim 14, wherein said liquid ammonia tube further comprising a freezer section upstream of the intermediate section, said freezer section being contiguous with said heat exchanger, wherein heat is exchanged between flowable fluids flowing in said freezer section and in said heat exchanger.
 16. A refrigerator according to claim 15, wherein said inner tube of the heat exchanger includes an outer surface, and said outer tube includes an inner surface, said outer and inner surfaces each having serrations to produce an increase in surface area of the corresponding surface. 